as we have seen, if I build the basic filesystem back into a single xzm file with dir2xzm, the resulting large xzm module is very slow to boot and heavy on the limited resource of an older machine.

Porteus modules from /base folder contain updated caches (gtk, pango, mime, etc..) so updating of these can be skipped resulting in a faster boot.
please have a look on /opt/porteus-scripts/xorg/update-cache script which is run when other than /base modules are discovered by booting scripts.
if you are able to add all caches to your custom modules then you could place them in /base folder and name as 009x- so it would be treated as native porteus module and not external one.
this action should make booting nearly as fast as it's with stock porteus modules only.

I really would like to do this, as it would speed up things greatly at boot up on my older hardware.
I've looked at the /opt/porteus-scripts/xorg/update-cache script and understand what it is doing.....
but I'm a bit confused as to what specific steps to take to add all caches to my custom
modules so that they can be placed in base with name 009x-.... Could you please explain
the steps to go through to do this? Thanks...

Thanks a lot! Could you please also post the list for 32bit arch? (that's what I use, for both full Porteus and Xfce.)
This is *very* useful information for Porteus users....perhaps it should be made available in the How-To section.

@claude
list for 32bits is the same, please replace every instance of 'lib64' with 'lib' and 'x86_64' with 'i486'.

This is *very* useful information for Porteus users....perhaps it should be made available in the How-To section.

i wouldn't do that cause users may start renaming their all modules with 00* (for faster boot) and that would certainly break some things at some point.
let's consider this as a 'secret porteus knowledge'

anyway - i'll be looking at update-cache script and try to optimize it to maximum so delays wont be that much of hassle.
will try to do that before rc2.